Miners want to tap subsea deposits of cobalt and other rare metals for green technologies, but environmental campaigners are worried

Gerard Barron brandishes a small black rock — the size of the palm of his hand — and heralds it as the future: “It’s all right here, all the metals we need.”

The Australian entrepreneur believes these rocks, formed over millions of years at the bottom of the ocean, can help satisfy the growing demand for the metals used in batteries and clean energy technologies, and are therefore critical to the transition away from fossil fuels. Less than 20cm wide, the so-called nodules can contain nickel, manganese, copper and cobalt— all set to see a surge in demand over the next decade.

Mr Barron’s start-up, DeepGreen, which is backed by shipping group Maersk and Switzerland-based miner Glencore, plans to suck up thousands of tonnes of the nodules from the sea floor using harvesting vehicles, and send them up a pipe to a ship to be sorted. Mining in the deep sea (defined as below 200m) can avoid the problems of land mining, he says, such as deforestation, pollution and child labour, although critics say it produces a whole new raft of problems.

“There’s no point thinking you’re doing the planet a favour by driving an electric vehicle if those materials have been mined by the hands of children,” he says, “or you have had to deforest important rainforest assets.”

The US Geological Survey says the deep sea, which covers around half of the earth’s surface, contains more nickel, cobalt and possibly rare earth metals than all land-based reserves combined. Mining can be legal in a country’s coastal waters, but is not currently in international areas.